linux/kernel/bpf/percpu_freelist.c

/* Copyright (c) 2016 Facebook
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of version 2 of the GNU General Public
 * License as published by the Free Software Foundation.
 */
#include "percpu_freelist.h"

int pcpu_freelist_init(struct pcpu_freelist *s)
{
	int cpu;

	s->freelist = alloc_percpu(struct pcpu_freelist_head);
	if (!s->freelist)
		return -ENOMEM;

	for_each_possible_cpu(cpu) {
		struct pcpu_freelist_head *head = per_cpu_ptr(s->freelist, cpu);

		raw_spin_lock_init(&head->lock);
		head->first = NULL;
	}
	return 0;
}

void pcpu_freelist_destroy(struct pcpu_freelist *s)
{
	free_percpu(s->freelist);
}

static inline void __pcpu_freelist_push(struct pcpu_freelist_head *head,
					struct pcpu_freelist_node *node)
{
	raw_spin_lock(&head->lock);
	node->next = head->first;
	head->first = node;
	raw_spin_unlock(&head->lock);
}

void pcpu_freelist_push(struct pcpu_freelist *s,
			struct pcpu_freelist_node *node)
{
	struct pcpu_freelist_head *head = this_cpu_ptr(s->freelist);

	__pcpu_freelist_push(head, node);
}

void pcpu_freelist_populate(struct pcpu_freelist *s, void *buf, u32 elem_size,
			    u32 nr_elems)
{
	struct pcpu_freelist_head *head;
	unsigned long flags;
	int i, cpu, pcpu_entries;

	pcpu_entries = nr_elems / num_possible_cpus() + 1;
	i = 0;

	/* disable irq to workaround lockdep false positive
	 * in bpf usage pcpu_freelist_populate() will never race
	 * with pcpu_freelist_push()
	 */
	local_irq_save(flags);
	for_each_possible_cpu(cpu) {
again:
		head = per_cpu_ptr(s->freelist, cpu);
		__pcpu_freelist_push(head, buf);
		i++;
		buf += elem_size;
		if (i == nr_elems)
			break;
		if (i % pcpu_entries)
			goto again;
	}
	local_irq_restore(flags);
}

struct pcpu_freelist_node *pcpu_freelist_pop(struct pcpu_freelist *s)
{
	struct pcpu_freelist_head *head;
	struct pcpu_freelist_node *node;
	unsigned long flags;
	int orig_cpu, cpu;

	local_irq_save(flags);
	orig_cpu = cpu = raw_smp_processor_id();
	while (1) {
		head = per_cpu_ptr(s->freelist, cpu);
		raw_spin_lock(&head->lock);
		node = head->first;
		if (node) {
			head->first = node->next;
			raw_spin_unlock_irqrestore(&head->lock, flags);
			return node;
		}
		raw_spin_unlock(&head->lock);
		cpu = cpumask_next(cpu, cpu_possible_mask);
		if (cpu >= nr_cpu_ids)
			cpu = 0;
		if (cpu == orig_cpu) {
			local_irq_restore(flags);
			return NULL;
		}
	}
}